1. Balancing Chemical Equations and Types of Chemical Reactions

2. Chemical Reaction
A change in matter in which one or more substances create new substances.
Reactants - substances that are about to react
Products - new substances produced

3. Law of Conservation of Mass
The total starting mass of the reactants equals the total final mass of the products.

4. Chemical Equation
Uses chemical formulas and symbols to describe a chemical reaction and its products.

5. Symbol
Meaning →
Yields or Produces +
Plus
(s)
solid
(l)
liquid
(g)
gas
(aq)
aqueous (dissolved in water)
heat, light, or electricity applied to reactants

6. Chemical Equation
Coefficients - Numbers that represent the number of units of each substance in a reaction.
Subscripts - numbers that represent the number of atoms of each type of element present in a molecule

7. Balancing Chemical Equations
Balanced chemical equations have the same number of atoms of each element on both sides of the equation.

8. Balancing Chemical Equations
Step 1 Count the number of atoms of the reactants and products
Step 2 Choose coefficients that balance the equation (Hint: Generally, if there is an even number of an element on one side and an odd on the other, place a 2 in front of the compound containing the odd number of atoms.)
Step 3 Recheck the number of atoms on both sides of the equation and adjust coefficients if necessary.
Remember when balancing an equation, only change coefficients. Do not change subscripts.

9. Diatomic Molecules
There are 7 elements that will only exists as diatomic molecules in nature and therefore in chemical reactions.
To identify them, the first six start at element 7 and make a 7 on the periodic table. The seventh element is hydrogen.
N2, O2, F2, Cl2, Br2, I2, and H2

10. Examples
H2 + O2 → H2O
MgCl2 + Na → NaCl + Mg
H2O + CO2 → C6H12O6 + O2

11. TOTD
Correctly identify the parts of this chemical equation.

12. Types of Chemical Reactions
Synthesis
combination of 2 or more substances to form a compound
only one product forms
A + B → AB
2P + 3 Br2 → 2 PBr3

13. Types of Chemical Reactions
Decomposition
a compound breaks down into two or more simpler substances
only one reactant
AB → A + B
2H2O2 → 2H2O + O2

14. Types of Chemical Reactions
Single Replacement
one element replaces another in a compound
metal replaces metal or nonmetal replaces nonmetal
A +BC → AC + B
Zn + 2HCl → ZnCl2 + H2

15. Types of Chemical Reactions
Double Replacement
ions in two compounds change partners
cation of one compound combines with anion of other compound.
AB + CD → AD + CB
2KOH + CuSO4 → K2SO4 + Cu(OH)2

16. Energy Transfer in Chemical Reactions
During chemical reactions
Energy is used to break bonds
Energy is released when new bonds are formed

17. Exothermic Reactions Reaction that releases energy by light or heat.
Products feel cooler than reactants
Ex. Combustion

18. Endothermic Reactions
Reaction that absorbs energy usually in the form of heat.
Products feel warmer than reactants
Ex. Chemical Cold Packs